There are known various methods and devices to treat pain both magnetically and electrically. Most of these methods have been used by physiotherapists and medically-trained personnel for treating pain, swelling and numerous other medical applications. Generally, these treatments involve the use of electrodes placed in contact with the body in the locality of the injury or pain sites being treated. Some of these prior art methods of therapy using electrical stimulation are disclosed in U.S. Pat. Nos. 4,117,846; 4,456,012; 4,765,310 and 4,846,181.
U.S. Pat. No. 4,117,846 (Williams) discloses a design of a disposable electrode assembly with indigitations to reduce overall cost and permit flexibility. It is suggested that in spite of the reduced surface area with the indentations, the electrode has approximately equivalent interface impedance as an electrode with continuous edges. The flexibility and free space between indentations of Williams' system also allow for greater adhesiveness between the electrode and body.
In U.S. Pat. No. 4,456,012 (Lattin) a design of an electrical device that generates both iontophoretic (direct current) and biphasic stimulation is disclosed. The circuit design allows for alternating the current type. It is indicated that this design is different as it incorporates the two current generators into one unit.
U.S. Pat. No. 4,765,310 (Deagle) is for the design of an electrode which delivers the combined and simultaneous delivery of transcutaneous electric nerve stimulation and magnetic field therapy. The disclosure of Deagle suggests that when used together the two modalities enhance each other.
In U.S. Pat. No. 4,846,181 (Miller) a technique of wound healing is defined in which high-volt direct current (galvanic) stimulation is applied with a generator that produces a rectangular-wave pulse of this type. The technique normally requires the initial treatment to have the active electrode over a wound be of negative polarity. On subsequent treatments, the active electrode is of positive polarity.
None of these prior art systems suggest the utilization of a switching device and an additional electrode in an interferential stimulation setup. By utilizing the teachings of the present invention the effective coverage is expanded substantially beyond prior art methods including that obtained by vector scan methods in current use.
Interferential therapy currently utilizes true interference of two medium frequency (over 1000 Hz) currents in the four-pole method and modulation of the intensity of a single medium frequency carrier current in the two-pole method. Both methods create intelligence waveforms or beats in the low frequency (under 1000 Hz) range using medium frequency carrier currents to be medically therapeutic. Both the two-pole and four-pole methods currently used have serious limitations.
The two-pole method permits a more specific selection of treatment location because the depth of modulation of the carrier current is 100% everywhere between the electrodes. Since the modulated current occurs even in cutaneous tissue, skin irritation may occur if current intensity is too high; see the article by M. Hogenkamp, Interferential Therapy, Enraf-Nonius, Holland 1983. In addition, the area of coverage is limited. The amplitude of the modulated current is diminished in areas that are not directly between the electrodes. A clinician may attempt to increase the size of the electrodes but as the edges of the two electrodes get closer together the path of least electrical resistance becomes more superficial.
The four-pole method allows for greater current intensities however there is a limitation in the area that is exposed to the effective modulated depths of the intelligence waveform. The area of the intelligence waveform is shaped like a four-petaled rosette with the axis of each petal offset to between the axes of the electrodes. Since the interference is reduced in the area where one carrier frequency current is dominant over the other carrier frequency current, the modulation depth is reduced and the treatment frequency is not effective in that region.
An attempt to overcome the limited treatment area with the four-pole method is the vector scan available on some interferential stimulators. With vector scan, the intensity of one of the carrier currents is modulated over time causing the petals of the rosette to move. This method does increase the treatment area, but the area about the electrode axes are still missed. With these limitations, diffuse areas of pain or poor electrode placement reduces the effectiveness of these three prior art methods of electrical stimulation.
The four-pole, two-pole and vector scan prior art devices and methods are all available via the Enraf Nonius Delft model Endomed 433 interferential stimulator manufactured by B. V. Enraf-Nonius, 1 Rontgenweg, P. O. Box 483, 2600 Al Delft, Holland.